1. The Field of the Invention
The present invention is related to structures which incorporate multiple resin systems yet which are mechanically integral. More particularly, the present invention relates to structures and methods which are capable of incorporating chemically dissimilar resins within a single integral structure by means of a three-dimensional cloth.
2. Technical Background
Laminated composite structures are used in many different environments. Such structures are often referred to by the generic designation fiberglass. Structures of this type are generally composed of layers of a polymeric resin along with some type of supporting structure. The supporting structure is often a fibrous material of various types. A wide variety of products are produced using these types of materials. For example, most conventional boats are constructed of these types of materials. Other similar products include rail transportation cars, car bodies, consumer products, some types of building materials, and components for larger structures.
In order to achieve a desired balance of physical, chemical, and mechanical characteristics within the structure, it is often necessary to layer materials. For example, it is not uncommon to include a layer of structurally strong material with a layer of material that may not be as strong but which provides an attractive finish. Similarly, it is often desirable to provide a layer of material that can act as a fire break in combination with other materials. As a result, the overall structure may include a plurality of layers including structural materials, fire breaks, and finish layers. In this way it is possible to take advantage of the structural features of a strong structural material, while still producing an attractive end product, or one which is not prone to ignition during a fire.
In general, such structures often incorporate three or more separate layers having distinct mechanical and chemical characteristics. A typical example may include a gel coat which results in an attractive finish, a fibrous mat, a structural conglomerate layer which includes a quantity of fibers, and a more solid backing layer.
One of the difficulties encountered in manufacturing this type of structure relates to bonding multiple layers together to form a single structure. In most cases, adhesives are used to bond the layers together. Thus, the final product results in layers of adhesives interposed between each of the structural layers.
When materials are layered in this manner several problems are observed. For example, when layers are bonded together with adhesive it is not uncommon for the layers to separate. This is especially prevalent in structures which are subjected to very rigorous environments, such as boats and other vehicles. When the layers separate, "delamination" is observed. This phenomenon is clearly disadvantageous. At the least, the structure looses its attractive finish. At worst, the structure is no longer structurally sound or useful.
Alternatively, the layer may be held together with mechanical fasteners such as bolts, rivets, screws, and the like. There are obvious problems with this type of attachment. Since the mechanical fasteners are generally much harder than the composite materials, the composites have a tendency to wear in the area of the mechanical fastener. Thus, the layered material will eventually fail because of wear between the mechanical fastener and the composite.
Problems with attachment of layers of composite materials is particularly acute when chemically incompatible resins systems are used. Chemically incompatible materials can generally be defined as materials that will not significantly cross-link during curing. In such cases it is clearly necessary to bond the two systems together mechanically or with an adhesive because chemical interaction between the layers themselves is not possible. Yet it may be difficult to achieve adequate bonding using a single adhesive due to the characteristics of the resins used. In addition, it is difficult to achieve an adhesive bond that is as strong as the remainder of the structure. As a result, failure of the bonded area is often observed.
Thus, it would be desirable to bond certain types of chemically incompatible systems together in layered composite structures without using mechanical connections or adhesives of the type described above. For example, polyester systems can be made to be cosmetically attractive, but often lack the desired strength to form a structural component. At the same time, epoxy systems are known to be strong, yet may lack the desired appearance. Thus, it may be desirable to bond a polyester system to an epoxy system in order to achieve structural integrity and an attractive appearance. In the past this approach has had limited success because these materials are generally chemically incompatible and chemical bonding is problematic at best.
Similarly, as mentioned briefly above, it is at times necessary to provide a flame and smoke barrier in a laminated structure. In those cases it would be helpful to include a layer of a phenolic-based resin system. Phenolics are known for their ability to resist combustion. It may be desirable, for example, to combine these features with the strength of an epoxy system. Again, however, phenolics and epoxies are not chemically compatible and must be bonded together by the use of adhesive or mechanical fasteners.
Accordingly, it would be a significant advancement in the art to provide methods for joining two or more resin systems into an integral structure without the necessity of adhesives, mechanical fasteners, or other conventional joining methods. It would be a related advancement to provide means for joining materials with different desirable characteristics, while substantially avoiding the possibility of delamination of the material. In that regard, it would be useful to have means for joining two chemically incompatible resin-systems without the need to employ adhesives and the like.
Such methods and structures are disclosed and claimed herein.